(a) Field of the Invention
This invention relates to an apparatus for the insufflation of gas into a body cavity, more particularly, of the kind in which the dynamic pressure of the gas flow conducted to the body cavity and the static intra-abdominal pressure in the body cavity are detected with at least one measuring transducer of which the electrical output signal for detecting the pressure is converted by difference formation with a compensation signal, which substantially takes into account the resistance to flow of an instrument for conducting the gas into the body cavity, into a difference signal which corresponds to the static intra-abdominal pressure and with this signal a control circuit for the adjustment of the desired pressure value in the body cavity is controlled.
(b) Description of the Prior Art
A special problem with the insufflation of gas into a body cavity, for example during a surgical operation, consists in generating with the gas flow a constant intra-abdominal pressure within physiologically acceptable limits and in measuring this pressure accurately. In the case of modern apparatus of the aforementioned kind, the supply of the gas into the body cavity and the measurement of the static intra-abdominal pressure is effected utilizing a single tube or pipe. Thus, for example, DE-PS No. 30 00 218 discloses an insufflation apparatus in which, in an internal operation, gas is insufflated through a supply pipe, after that the gas flow is switched off and then the pressure through the same pipe is measured. This method involving intermittent gas inflow and pressure measurement by way of a supply pipe leads perforce to a regular interruption of the gas flow and can lead to exceeding the desired value, to be preselected, of the intra-abdominal pressure, namely when a gas flow phase starts just before the desired pressure value is reached.
Equally, in the device disclosed in EP-OS No. 0 169 972, merely one pipe is provided for the gas flow and the pressure measurement. In this specification it is proposed, after a single compensation, undertaken at the start of the entire insufflation procedure, of the system resistance, which is dictated mainly by the instrument projecting into the body cavity, for example a Veress needle, constantly to ascertain the static intra-abdominal pressure by the substraction of the system resistance pressure from the total pressure and to indicate same to the doctor. This proposal has however, the disadvantage that a change in resistance, caused for example by a change of instrument, a retrocession of the flow as a result of low pressure difference between inlet and outlet or by kinking of the hose is not taken into account during the continuance of the insufflation procedure.